Optimising Building Design for Sustainability Using High Performance Concrete

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Optimising Building Design for Sustainability
Using High Performance Concrete
Doug Jenkins - Interactive Design Services Daksh
Baweja The University of Technology,
Sydney. Joanne Portella DMC Advisory, Melbourne.
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Introduction

• Focus of emissions reduction strategies in
  Australia has been on cement reduction.
• Can significant emissions reductions be made with
  the use of high strength concrete?
• Outline of study
• Effect of high strength concrete and high
  supplementary cementitious material (SCM) content
  on total CO2 emissions.
• Typical flat slab building structure
• 5 grades of concrete
• Reinforced or post-tensioned slab

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Alternative Concrete Mixes
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Component Emissions
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Embodied Energy Calculation
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Concrete Emissions Analysis

• Emissions based on emissions of component
  materials multiplied by material content
• Cement emissions allow for 5 mineral additions
• Total mix emissions mainly controlled by cement
  content
• Based solely on emissions per cubic metre of
  concrete, the 25 MPa standard structural mix, and
  the 40 MPa high SCM mix appear to offer the
  minimum CO2-e emissions.

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Flat Slab Layout
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Structural Design Procedure

• Design to AS 3600 simplified method.
• Checked to equivalent frame method (Warner et al)
• Prestress force balanced approx. 85 of dead load
• Deflections checked with non-linear finite
  element analysis

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Slab Sections

• Reinforced slab depth controlled by deflections
• 25 MPa 300 mm
• 40 and 65 MPa 250 mm
• Prestressed slab depth controlled by punching
  shear
• 40 MPa 180 mm
• 65 MPa 170 mm

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Deflection Analysis

• Non-linear finite element analysis 4 node
  plate-shell elements
• Stress-strain curve formulated to give correct
  moment-curvature behaviour, allowing for
• Cracking of the concrete
• Tension stiffening and loss of tension stiffening
• Long term creep and shrinkage effects

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Typical FEA Mesh
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Vertical Deflections, Slab 1-B
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Vertical Deflections, Slab 1-C
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Vertical Deflections, Slab 2-C
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Deflection Results

• Long term deflection of reinforced slabs greatly
  increased due to flexural cracking, shrinkage and
  creep effects
• Deflections of prestressed slab greatly reduced,
  and increase in deflection with time much less
  because the section remains uncracked.

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Emissions Analysis Results
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Emissions Analysis Results
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Conclusions

• The mixes with minimum emissions allowed a small
  reduction in CO2 emissions for the reinforced
  slabs, compared with the standard reference
  case concrete.
• All of the prestressed slabs showed a much more
  significant reduction in total emissions, in
  spite of the higher cement content of the
  concrete used.
• The high SCM 40 MPa mix gave the lowest overall
  emissions with a prestressed slab, but the
  emissions from the 65 MPa mix were only
  marginally higher.

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Conclusions

• Higher strengths allowed the use of a reduced
  depth of slab, with associated savings in other
  works. These savings were not included in this
  analysis.
• The high SCM mixes had a reduced early-age
  strength which is likely to impact on the
  construction program.

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Conclusions

• The overall reduction of CO2 emissions was not a
  simple function of the reduction of Portland
  cement in the concrete, but was also based on how
  the material properties of the concretes used
  influenced the structural efficiency of the
  design.